1. In 1994, Lemieux entered the Chicoutimi Conservatoire de musique and began studying voice with Rosaire Simard.

1. In 1994, Lemieux entered the Chicoutimi Conservatoire de musique and began studying voice with Rosaire Simard.
Marie-Nicole Lemieux graduated with a Masters in Vocal pedagogy in 2000.
Marie-Nicole Lemieux won first prize at both the Jeunesse Musicale du Canada's Joseph Rouleau Competition in Montreal and the Queen Elisabeth International Music Competition for Opera in Brussels in 2000.
Marie-Nicole Lemieux took second prize in the separate competition for Lieder at the Queen Elisabeth International Competition.
Marie-Nicole Lemieux has sung with conductors such as Richard Bradshaw, Franz-Paul Decker, Charles Dutoit, Paul Goodwin, Bernard Labadie, Sir Neville Marriner, Kurt Masur, Marc Minkowski, Kent Nagano, John Nelson, Gianandrea Noseda, Peter Oundjian, Michel Plasson, Federico Maria Sardelli, Michael Schonwandt, Marc Soustrot, Yoav Talmi, Ilan Volkov and Pinchas Zukerman among others.
Marie-Nicole Lemieux has received praise for her stage presence and communicative power.
In 2002, Marie-Nicole Lemieux made her professional operatic debut in the role of Cornelia in Handel's Giulio Cesare with the Canadian Opera Company.
In 2006, Marie-Nicole Lemieux appeared as Alisa in Donizetti's Lucia di Lammermoor with Opera de Orange and Anna in Berlioz's Les Troyens with Strasbourg Opera.
Marie-Nicole Lemieux performed the title role in Vivaldi's Orlando furioso at the Edinburgh Festival.
In 2008, Marie-Nicole Lemieux sang the title role in Albert Roussel's Padmavati at the Theatre du Chatelet, Genevieve in Debussy's Pelleas et Melisande at the Berlin State Opera, the title role in Handel's Orlando at De Nederlandse Opera, Mistress Quickly in Verdi's Falstaff at the Theatre des Champs-Elysees, and Marthe in Gounod's Faust at the Opera de Orange.
In 2009, Marie-Nicole Lemieux sang Genevieve in Pelleas et Melisande at the Theater an der Wien, Mistress Quickly at the Bavarian State Opera and the Glyndebourne Festival, and Zita in Gianni Schicchi at the Opera de Montreal among other engagements.
In 2015, Marie-Nicole Lemieux was appointed a member of the Order of Canada.
In July 2022, Marie-Nicole Lemieux performed Saint-Saens, Massenet with the Monte-Carlo Philharmonic Orchestra at the Prince's Palace, Monaco.